Popular in Biology II: Ecology and Evolution
Popular in Biology
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Date Created: 08/19/15
alto hg LECTURE 8 TROPHIC INTERACTIONS 11 EFFECT ON PREY POPULATIONS ie hold g capacity Key question J x x w i w a a numbers of prey down below envzronmental carryin Prior to 1216 Widely assumed that since predators remove prey from environment predators must reduce prey to lt K In other words the more predators the fewer prey and vice versa Graphical representation of the pre1946 conventional wisdom wout predators PM quotquotquotquotquotquotquotquot quot ab J w predators QM TIME gt Doomed surplus hypothesis 1946 Paul Errmgton argues there are Sltuatlons 1n wh1ch predators are not expected to limit abundance of prey below K He argues gt In some cases population growth rate of pre rowth rate of predator f Qfar outwei gt Aopopulatlo lululiw t jlnl s mural more food for predators 9 higher birth rateslower mortality rates gt However because of diferent rates of ction 39 m 4 39 39 39 quot 739 39rl 4ml 4 ml quotH quot ml 7quot quot 4 r 4 397 39 lll Hl w ll ill llll ll 5 lll Hl As such predators may slow growth of prey pop but will not stop prey population from reaching K prey population size will ultimately be limited by resource availability intraspecific competition QZQ angels x cm Errington looked at mice high reproductive rate 6litter multiple littersyear Their predator kestral produces at most 34 offspring bType survivorship curve Graphical representation ofErrington S idea wout predators c w predators a O I II I I I I I I I I I 0 TIME gt 9 MW SV V 3505 gt Errington notes that populations of many prey spec1es g x099 overreproduce during summer months When food is abundant produce more offspring than can be supported by the available resources in the coming Winter YSSpringtime lots of resources available seeds babies gt This causes especially come Wintgrintraspec1f1c competitlon and nancompetitive individuals 6 g the very young the very old the weak amp sick to die from aggression starvation exposure other causes Errington calls these losers in intraspeci c competition the 100de surplus quot Not getting enough resources to meet maintenance PICdators a if a r i i Eiigil iirl I l a M 313 mi 06 a 09 tany indiv that is less competitive Big question Was Errington correct Do predators sometimes fail to hold prey numbers down below the prey population s environmental carrying capacity Great Horned Owl ranchers shoot them to protect Ringnecked Pheasant Testing Errington s Doomed Surplus hypothesis predator removal experiments A faulty approach used in early tests Estabish predator removal site and count number of prey on site Trapkiremove predators for some period of time At the end of that period assess number of prey If number of prey increased they would conclude that the predator was reducing the prey population Problems with this approach 1 If you see increase in prey population size can you be sure that this resulted from a lack of predators Popuations of prey may uctuate for a variety of reasons unrelated to predation What if gtMore food resources 2 Prey populations may at 3 6 W Prey N 1 6 time ma A better approach Establish experimentalpredator removal areas but also establish control areas identicalsimilar bioticallyabiotically to expt areas Predators are left at their natural abundance in control areas Count prey at both sites and monitor prey populations over time Some possible results xpt area Q control area X Yr S 39 Rg m MIQNOQ prey cf PV thnesa thnesa Prey thnesa thnesa 9f7 7 lt t 9quot wbwwwm 3 Examples of predator removal experiments 1 Foxes and bush rats in Australia Red foxes introduced from Europe to Australia to help control introduced rabbits Now major concerns about impact of foxes on native mammals such as bush rats predator red fox Experimental design Six 39 large research plots 1018 km2 in Namadgi NP east Australia Two experimental plots foxes poisoned Four control plots no poison Fox numbers redch in expt plots within 18 months Fox density 5x higher in control plots 3 foxes per km2 Relative density of bush rats monitored 2 yrs using baited live traps 15 traps placed at two sites in each plot in preferred habitat opened 3 consecutive nights every 2 months Results ID00 control sites 25 Q q fox removal sites No 20 H of rats 15 trapped IO 5 p 0 l l i l l l J l l l l l l Apr93 Aug93 Dec93 Mar94 Aug94 Nov94 Mar95 Summary of results lntraspeci c competition limits population to it39s carrying capacity Pop uctuates so most likely overshooting its K doomed surplus Same that pred would have eaten would have died anyway Conclusions Researcher writes quotDensity dependent resource limitation may have prevented further population growth in experimental areasquot Researcher writes Density dependent resource limitation may have prevented farther population growth in experimental areas Gra wolf and Alaskan moose cow and calf V w 9 a 7 ti 39 397quot Alaskan moose bull 2 Predation on moose by wolves in central Alaska AK Fish amp Game biologists set up 17000 km2 quotexperimental areaquot Severely reduce wolf gs in area from 1916103 by shooting Also have several quotcontrolquot areas no wolf reduction But primarily compare moose survival abundance in expt area beforeafter wolf reduction program l x T TAN3M4 HILLS Control Areos h U f I f FORTYMILE RANGE ComingI Car39bou quotAreo I I DENALI NATIONAL PARK Fig 1 Study area in interior Alaska Experimental area with wolf reduction and control areas without wolf reductiorl are 39 outfitted in solid and dashed lines respectively StUdy Stopped after 3 yrs bc controversy over killing of wolves Resu s to remove from exp areas a Prior to expt estimated 240280 wolves in expt area Wolf numbers drop gradually each year to 5080 animals b See dramatic increase in percent of moose cows w quotvearlingsquot Avg for 19731975 16 if Ev 39 9 Avg for19761979 43 wh 31 so x014 1 Wu fly Ev 3095 90R c Study of radiocollared moose shows substantial increase in survivorship of older adult moose Percent dying per year no animals radiocollared Moose ade vears 197375 19761979 1 5 0 6 0 14 610 33 6 7 29 31 0 o X Q s gt11 41 o 7 21 o 56 49 30 1W End result Increased survival of calves and older adults causes substantial increase in moose abundance Estimated moose abundance in experimental area 1975 2800 gt ancrease in abundance Later studies show moose population continues to increase in numbers into the 1980s 1978 3500 Control areas show no increase in calf or adult survival from 19761979 and presumably no changes in moose abundance Conclusions The evidence supports the hypothesis that the wolves predators are reducing the moose population gt100 predator removal studies have been done The Doomed Surlus hypothesis was supported in some cases E Raises the question What determines Whether a specific predator Will limit abundance of a specific prey species Key factor as Errington recognized Reproductive patterns of prey and predator species Potential population growth rate of the prey species vs the predator species Population growth rates depend heavily on 3 things 1 No of offspring produced per breeding attempt litter size 2 No breeding attempts litters annuaHy Potential population growth rate of prey vs the predator 3 Generation time time bt birth of female to birth of female39s own young r Prickly per cctus 5 r PIC treatment i39 1 wquot 39 39 th F v 391 39 t 1 u 4 3quot 39quotquot 39 g 396 I Q I v u U BIOLOGICAL CONTROL ductions of species into areas beyond the range of their natural enemies can result in explosive episodes of population growth I that create ecological and economic problems Control of such introduced pests is sometimes obtained by the controlled introduction of a specialized predator Some Of the best examples of biological control involve the control of introduced plants by invertebrate herbivores and the control of an intro duced herbivore by a viral pathogen 39 Two species of prickly pear cactus Opzmtia inermis and Opuntia stricta became important pests after their introduction into Australia where they apparently had no effective natural enemies Dodd 1959 Opuntia popula tions grew rapidly and transformed many in Some evidence for the importance of areas of rangeland into impenetrable 6 predation comes from examples of thickets Cactus thickets offered very poor biological control grazing for livestock which provided an economic incentive to control cactus abundance In an effort to control the cactus outbreak the herbivorous moth Cactoblastis cactorum was introduced into Australia from its native range in Argentina Larval moths feed only on cactus and in the process of feeding burrow through the cactus and make it susceptible to infection by other pathogens The introduction of Cactoblastis caused a spectacular decline in the abundance of cactus Opuntia is now greatly reduced in abundance through many parts of Australia where it was previously a nuisance and it now coexists with low densities of its natural enemy in a sort of patchy game of hide andseek A second example of the successful biological control of an introduced plant by an herbivore involves St John swort Hypericum perforatum in Cali fornia Huffaker and Kennett 1959 Hypericum is another serious rangeland pest although for somewhat different reasons than Opuntia Hypericum con tains phototoxic chemicals which when eaten by cattle cause the cattle to become highly sensitive to sunlight This sensitivity results in the develop ment of skin lesions that make the cattle unmarketable To control Hyper icum the specialized herbivore Chrysalina a chrysomelid beetle was introduced into regions infested by Hypericum Larvae of the beetle burrow into the roots and stems of the plant killing it The beetle was a spectacularly effective control agent and eliminated the plant from most habitats except for shady sites where the beetle does poorly and the plant manages to hang on A v131tor to California who was unaware of the history of this ongoing interac tion could easily but wrongly conclude that Hypericum was a specialized shadeloving species since it seems to now be found mostly in shady sites where Chrysalina is an ineffective predator Hypericum is of course restricted to those sites bya relatively inconspicuous predator that is now at low abun dance throughout the plant s range because of its success in keeping its spe cialized food plant at low abundance WigVb LECTURE 9 THE NATURE OF BIOLOGICAL COMMUNITIES Ecologists rarely study an entire community have to focus on speci c subset of populations Biological community an assemblage of populations of different species living in a prescribed area DEFINING CHARACTERISTICS OF COMMUNITIES 1 Species Composition A Membership list who39s present and who39s not B Species richness and diversity species richness refers si m ply to th e i in community ignoring relativ a undances species diversity refers not only the but also til 4 v individuals belonging to each species a community with more even numbers of individuals in different species is more diverse Imagine have two communities each w four spp A B C D Number of individuals of each species Community 1 25 A39s 22 8393 30 0393 23 D39s Community 2 6 A39s 84 8393 1 C 9 D39s Two communities are equal in species richness 4 but which community is most diverse Community One is the most diverse 2 Physical structure or quotphysiognomyquot of community overall quotphysical structurequot of community Determined by quotgrowth formquot of predominant plant species number of vertical layers of vegetation amount of surface covered by vegetation Think of Low of seedlings Oregon ridge bc of large deer population very small amount of surface cover Conservation vs Preservation Tropical Rainforest in Costa Rica Predominant species type is tree 789 levels of vegetation vines canopy subcanopy etc of ground cover is very high SteppeGrassland Russia Predom species type is grass 1 level of vegetation Moderate ground cover 3 Trophic structure basically who eats whom Described using foodtrophio Chains and webs W U vl M UR I c4 3 Carnivores lt gtCarnlvores I Zooplankton Herbivo Plants I Phytoplankton MS Primary m consumers reducers Remember lecture 2 Snowshoe hare amp lynx Why do they cycle Where do hares t in the trophic structure of Part of the food web in the Canadian Arotiow W21 golden hawk owl eagle harder moose small red ground willow sp e passerine rodents squimel l ptarmigan rouse birds insects fungi f b bog grey white balsam or 8 gmbse birch willow I soaprH spruce poplar aspen Many herbevores will opportunistically eat babies of other species 4 Productivity and pattern of energy flow through community How much new quotbiomassquot living tissue is produced per year by plants and by animals 5 Input output and recycling of essential nutrients All organisms need certain key nutrients eg N P Ca Mg 8 Fe Animals get essential nutrients from food plants or other animals Where do the plants get the nutrients they need A key point about the nature of biological communities Populations in communities are tied together in a very complex web of both direct and indirect interactions Each species in a community interacts directly with a variety of other species Direct interaction where the activity of one species directly affects the survival growth andor reproduction of individuals in another species Types of direct interactions e g bison population of Wind Cave National Park Black Hills SD Microparasites Predators Mutualists viruses bacteria coyotes cougars cellulosedigesting amp protozoans I microorganisms in gut i 7 39 2 l w 39 Macroparasites Prey Competitors ticks lice fleas grasses herbs mice grasshoppers flies flukes worms shrubs tree seeds deer beetles antelope Indirect Interactions Between Species Indirect interaction where the activity of one species affects the survival growth andor reproduction of another l A l One example of an indirect interaction between species C p a trophic cascade Wf v f ybbobw 3 71 1Q 5639 Definition when a consumer species not only has a direct negative effect on the trophic level below it ie on its prey but its actions also affect species in trophic levels below that Wm Mgov In other words The effects of the consumer species cascade down through several trophic levels 1 ampLquotDm n uh le for example 6 3 OVC QNQ predator e aa klnA 1 b l 39 H I M Q r indirect W 02 I herbivore erg 4quot DOSItlve 3053 Q direct interaction 1 Effect Hidirect negative effect quotIf ck indirect interaction i ll ION 9 a A plant Aggy wimo gawbg m Note Depending on the system the consumer species could be a predator parasite or pathogen pawsans 4 indirect negative effect Row GMV00 Wellstudied trophic cascade in th Aeutian Islands Alaska 397quot quoti D i 39V fu gt o 39 X 39 If M x s 39 404 Sea Otters 0quot l 39 l 39 5 vi 23 g Y397 J 7 Q9 I All Sea Urchlns 9 o I I I direct interaction x yr indirect interaction I l l I x H Brown Kelp 402 GM ob 0 Coka my O Owo fw 002536 It is actually a lot more complex than this Summary of some of the direct and indirect effects of species on one another in the Aleutian Island Ecosystem MVX N5 WW W Humans WK v predation N C 43W w Great Whales a X0 6 05 we I I 9 U9 pquot a predation a 0 wwa x Killer Whales I I I x X predation 1 r I I r I I 4 I I Sea Otters N I x x 5 predationl g I I A Sea Urchrns I I l a 1 l I predation I l I I I 39 e I E Brown Kelp i I predationT I N I r I 1 Rock Greenlllrgg 4 gwlqu 70 2 V 0 direct interaction 1 MM 05 indirect interaction I x Anoert e of indi ect interaction between species cic39wggc if fu xji T72 39 HuiExwrj 53317TIquot fwrgm lgl lgr39jjftquot39u ll till ell till l ll QM Two Definition where a quotconsumerquot species mediates affects the outcome of competition between two or more species Usual reason the consumer preys on the stronger competitor thereby making more resources avail to the weaker competitors gA afRSVWSaSX QA QUAWVSGA MUSSQAQ Hypothetical example Imagine three species of aphids all feed on photosynthate in black gum leaves strongest 60 le VJ 3M Photosynthate flowing out of black gum tree leaves WL N MM Optimal position on the leaf Where all transport vessels carrying photosynthate INCH do conver e occu iedb stron est com etitor resent g p y g p p oums bC WVK COMUW A Now imagine that there is a parasitoid in community that attacks aphid species X primarily or exclusively What direct and indirect effects Will the parasitoid haVe Direct negative effect on aphid X pop indirect positive effect on Aphid Y You are al advf miliar with the fundamental concept behind m fa illlliiill Recall that TWO things determine the outcome of competition between two species competitive exclusion or stable coexistence 1 extent of niche overlap 2 ability of stronger competitor to grow a large pop and take all the resources away from the weaker competitor If some environmental factor limiting the abundance of the stronger competitor this can allow the weaker competitor to gain resources and coexist Previous example NW9 w How abundance of the stronger competitor affects the potential for species coexistence a classic example Recall Paine s experimental work in the 19605 involving competition for space on rocks among invertebrates in the intertidal zone ll Chitons Limpets Mytilus Acorn Mitela Sesszle spp b1valves barnacles must 2 spp 2 spp bivalve barnacies goose glue selves to rocks so they can lter bamac39e tiny organisms from water If not glued to rock will get washed away Several spp of invertebrates compete for space on rocks if don t get space they die because they can t feed 39 Mobile spp chitons limpets graze on algae that grows on bare rock if no bare rock no algae no mobile species Mytilus is the strongest competitor species can grow over top and starve out species thus can occupy mostall of bare rock HOWEVER one species of starfish preys on all sessile species gets most of its calories from eating Mytius mussels Consumer species especially top predators can often be keystone species within communities Keystone Species A species Which through direct and indirect interactions determine the abundances of large numbers of other species in the community and hence the biodiversity of the community Consumermediated competition ox W3 a real example No0quot 3 4 25 9 39 A79 W Ecosystem spring ponds in North Carolina Competitors larval stages tadpoles of multiple frog species Consumer Eastern redspotted Newt Notophthalamus viridescens Eastern Redspotted Newt Notophthamus viridescens Experimental design Put equal numbers of tadpoles of 6 frog species into 16 artificial ponds tanks four each with O 2 4 or 8 newts Results relative abundance of different species of metamorphosed A froglets at end of experiment a Cl H Q A O M D 0 Mean Relative A bun dance Io m c 0 Newt Density nutank gt Vquot quot Q 4 quot 3 39v39 r VY v V I It allowed weaker competitors to gain more resources and hence exist at higher abundances meant there was less risk of weaker species being competitively excluded Researchers also do quotprey preference testsquot with newts giving newts choices of different tadpole species Critical finding PtcviovsfiDao Et39niitcit39ai limium39uphs 532 I983 pp 119438 I933 by the Ecological Society of America PREDATION COMPETITION AND THE COMPOSITION OF LARVAL ANURAN GUILDS l PETER J Momn Department of39Zooiogy Duke University Durham North Carolina 27706 USA Abstract Experimental manipulations of densities of the predatory salamanders Notophthaimus riridesrens dorsaiis and Ambysmma tigrimtm signi cantly altered relative abundances of six species of larval anurans in 22 arti cialpond communities One competitively inferior anuran Hyia rmaw was virtually excluded from predatonfree control communities but39survived best and occmred at greater relative abundances in communities contain iiiwg mhigh d hSiii s of Notop hthaimus A39second comii 39t i39iiii iiquotquotiiii r39i r39 species Hyfa gramsu quot 39irite39nSItles of predation Each of four competitively superior species Sraphiopus hoibrooki Ram sphenocephaia Bufo ter restris and Hyiu thrysoreh39s exhibited inverse relationships between relative abundance and No tophthaimus density Ambystoma eliminated the entire anuran guild from tank communities and had a much greater per capita impact on anuran guild composition than did Notophrhaimus In most anuran species maximum and mean mass at metamorphosis were positively correlated with predator density suggesting an inverse relationship between intensities of predation and com petition among tadpoles Low growth rates of most anuran species in the absence of predators were correlated with high abundances of superior competitors These results indicate that predators me diated interspeci c competition among larval anurans Intermediate values of Notophthaimus density maximized the total production of anuran meta morph biomass Biomass of metamorphs of each species varied in a speciesspeci c manner with predation The propensity of Rana sphenoceph 39 39 flquot LECTURE 10 COMMUNITY COMPOSITION quotMEMBERSHIPquot IN ECOLOGICAL COMMUNLTIES 0 Communities appear to be like excluswe country clubs Dlt0ltW3 allowing only some species to join OJ 9 For example The tree community of Oregon Ridge Park Dofind But do not find Chestnut oak Bear oak Northern red oak Blackjack oak American beech European beech Black gum Sweetgum Red maple Sugar maple Sassafras Gray birch Tulip tree Atlantic White cedar Pi gnut hickory Bitternut hickory thequot quot ght a The Central Question in Community Ecology 139150 4 Kt Of all the species that could occur in a particular community what determines which species actually 6Q occur in the community Of most interest The role of interspecific interactions Note It situations where it is clear that eg girraffe in tean 493 451 propagules of an excluded species could reach the area asquot 2 the excluded 3 ecies could tolerate abiotic conditions in area 0 quot eg sea nettles in bays We have to assume that a species is not found in the area because some kind of biotic interaction is preventing that species from establishing a population How important are different biotic interspecific interactions in determining community composition Mpgquot C quotf quot 3 JR 7t 4 4 dgt 039 is 4 predation herbivory paras1t1smld1sease mutualism competition i thought to occasionally determine Whether a species occurs in a community a few known examples traditionally thought to be the most critical factor in most situations Competition Hypothesis F or most species what determines whether that species will or will not he in a communily is that species abictic conditionsresources and its Hypothetically two species that use the rescarce s in the basic way i e have same niche should not be able to 5 9C L OJ 7 1 c 9 5 0 0 0 Thus communities should consist largely of species that M use existing resources in different ways The Competition Hypothesis defined by hypothetical example 6 d 0 0 Imagine you have 3 specres of raptors In a communW Q zwtb 030 4m 39cl ifq 39 Redtailed Golden 93ka 3 Am Kestrel 638quot gut 6 Hawk Ea le 0 I 1 Kt o was We Number of prey of that size eaten 20 40 60 80 100 110 20 0 Size of prey animal grams ons 0 W Could a new species of raptor enter the community W00 Wt gJQ Q 03 new species ML Yes if it can consume an unutilized portion of the resource take an empty niche or if can competitivelv exclude an existing species but it should NOT be able to do this coexist in same niche size of prey animal Dqq3 What evidence would suggest that competition is indeed a key factor in determining community composition Prediction 1 of the quotCompetition Hypothesisquot If competition is critical in determining What species cooccur in a community then species that use the same basic resource and i coexist should show evidence of We 2e ma tuxo r ie they should divide up the resource in some way Potential competitors could use different part forms or portions of the same resource eg Raptors eagles kestrels use the resource in different places habitat or spatial niche partitioning eg Paramecium use the resource at different times of day season year temporal niche partitioning eg Owl coexisting with raptors nocturnal at night hunter Abundant evidence of niche partitioning exists Niche partitioning in Bats Holy Bats Batman 0 copyright J Scott Altenbach Researcher Raphael Arlettaz University of Lausanne Switzerland Organisms Greater mousecared bat Myotis myotis Lesser mousecared bat Myotis blythii Extremely similar species identical in size and external appearance can only be identified with certainty using DNA analysis Often find both species in a local area often sharing caves and other roost sites Both species feed by gleaning insects off of surfaces W Question How do these two species coexist in same location4 9 0 gt6 M39 80 60 Analys1s of fecal samples Percent of show two spec1es ut111ze diet 40 different prey species 20 0 lGrounddwelling insects beetles n Insects found on grass stems I M m yotis M blythii Grew LQASU ogtlt ax A5b Radiotracking of individual bats shows that two species typically forage in very different habitats in the local area I M myotis n 362 1ha cells 352 430 df 9 P lt 0001 M blythii n 381 1ha cells X a g ohns rnsgnslnsil w W AU lt2 we a 3 5 40 1 3 5 d L a so a I E E 20 a I 010 3 64 5 0M m X any g 40 03w 3 2 28 Habitat category 4039 Fig l Inter Speci c differences in the mean percentage frequency of utilization of the it main habitat categories see Table 2 habitats are ranked according to their approximate degree of clutter from left to right Chiasquare and randomization tests were carried out on overall absolute frequencies not on percentages of visited habitat categories number of lha Cells see Methods ns nonsigni cant P lt 001 P lt 0001 A ground gleaner M myotis forages in mowed meadows orchards forests A grassgleaner M blythii forages in grassland steppe pastures meadows Example Differentfeeding niches Offish in pools of a Panamanian stream Resource being partitioned insects other small invertebrates that live or fall into stream pools F LSURFACE Cross sectlon of a pool a showing feeding locations of W I 10 species occupying pools Tquot F i l 2 EDGE Astvanax M Spec1es 1n st1ppled area are 3 MIDDLE Roeboidea 39 Poecilia nocturnal species JVeohetezandr a I 1 M Electris39 Rhamdia u u 39 o u c 2 L M 352339 39b39fairidhus i 4 BOTTOM Spec1es Hunt1ng method and preferred food Aeqaia ens Picks anything live or dead off bottom Eleotris Sits and waits to ambush any large prey item suspended in water column Piabacina Actively chases down prawns Example temporal partitioning of resources owering times Ofdi erem animalpollinated plant species in Costa Rica What is the resource partitioned by the plants Answer pollinators like bees and hummingbirds that carry male gamete pollen to females parts of conspecific owers to assist in reproduction If there is too much competition for pollinators too few to go around then a plant might not get its egg cells fertilized can reduce fecundity In figure below each number refers to a different species of plant thin line represents complete range of owering times for species bar represents peak times 2 3 7 m 11 395 7 u 6 8 1o 9 l L l i l l l l I I J 2 1 4 v 5 395 e l 7 3 10 9 i l 1 l L I d l J I l l J F M A M J J A s o N D Months Summarytakehome message Different species of plants open their owers and use the pollinators services at different times of the year Prediction 2 of the quotCompetition Hypothesisquot If competition is critical in determining species membership in biological communities then species that would use the same basic limited resource in essentially the same way 2 high niche overlap it the same community To rephrase If you introduced a new species into a community that uses a limited resource in the same way as an existing member of the community one of two things should happen the new species should not be able to establish a population individuals can39t get enough resources for adequate survival growth and reproduction so K 9 onwwsggwaag 6002 0027 the new species establishes a population but in the process M competitively excludes competitor from community 93quot V x0 How could we test Prediction 2 0 f G I 09 7k 605 55 03 X 86 125 and g 00 by 0411 g X b 5 X9 i 5 13 N M L0 0 w 7on V 9 039 0 50 C 009i 5 0 99 we 8 5 60 6 000 0v DogLil 92w An quotaccidentalquot test of Prediction 2 Invasion of Great Lakes and Mississippi River drainages by the zebra mussel Zebra mussel gt native to the Caspian Sea in Eurasia arrives into Great Lakes 1988 probably in ship ballast H20 gt attach to any surface suck in water filter out tiny plants and animals plankton for food gt small 25 mm long can reach incredible densities 3000 50000 m2 gt will attach in large numbers to shells of native species fouling them ie intercepting food smothering intake valves Have had local extinction of native mussels as a result of invasion by zebra mussels One example Soulanges Canal St Lawrence seaway Canada 25 i 50 Dene y 39 20 3 Density of native 39 4390 Degree of zebra mussels 15 a i a mussel infestation 2 50 039 per m no zebra mussels M w j n 10 i for every 1 native 20 mussel present Infestation I h i Oquot 5 a i 10 NW 0 I I l l T ITI LI I I I I l C39 G V W Va axvgaemmeaeevzae de X L naggiaeeggeae aaag a f Jam 2 m 06 al 1a92 i993 i994 WQS Q 06quot gt0 o Sompling dote 9 0 THE COMPETITIVE EXCLUSION PRINCIPLE ALWAYS TRUE Explaining the Coexistence of Species With Seemingly Identical Niches Mid 197039s Researchers start to question the importance of niche overlap and competitive ability in determining species composition in some communities Why They observed that in some communities individuals with extensive niche overlap do coexist indefinitely 3 y W00 Example Galemcella leafbeetles 0n purple loosestrife plants 04105 Purple Loosestrife Large attractive aquatic plant native to Europe 3 introduced to US in early 1800s now found everywhere WA 4 f 2quot x A 1quot39 Prolific breeder Wplantyear a Seeds readily disperse Will totally outcompete and excluding native wetlands vegetation leads to loss of multitude of animals that depend on native A K0 vegetation also plugs up irrigation systems N 0 A major exotic pest species 151 difficult to eliminate quyxp 39 0 Da dj s wt is xix o gtlob gt quot 909 9 W Galemcella calmariensis amp G pusilla leaf beetles native to Old World Two leaf beetle the adults and larvae of which both feed on loosestrife v quot v a i i u At quot l Galemcella calmaiensis Galmcella pusilla Morphologically very similar but truly different species cannot successfully interbreed Adults feed on growing tips of purple loosestrife larvae feed on all above ground plant parts Being investigated as a possible biological control agent for NA populations of purple loosestrife ENquot X 4139 9 00quot 01 W QW 39060 Research by Swiss researcher Bernd Blossey 3 souqht evidence of niche partitioning to explain coexistence of the two species of GaeruceIa beetles in Europe worked at multiple sites in Germany in late 1980s early 1990s Results of his study on next pages Do the two species attack loosestrife in different habitats E both species 25 G pussilla only 03 I G calmariensis only MW 2 20 0 quot as 395 15 MD 5 o39 a z 10 5 0 I l Ditches Shorelines Wet pastures Marshes Conclusion Xxxlusv x No viabvrwra3 amp MW 2 Do the two species occupy different plants within habitats In Germany s W determined number of each species on 800 plants o 229 plants with gt1 adult beetle v gv Conclusion NOAF MM BS CUUQVTMRS 350 340mm saw tows Do the species attack loosestrife in at different times of year 250W El males 0 females G pussilla G calman39ensis Number of 150 adults found quoto 04 I June l Sen C s M w Conclulsgg MKML LNCKO3 Nclw R09 Ogt DO the two 3 20 O G pussila A SpGCi E 151 A Glcalmariensis 3 es F prod E w uce f WON B offsp 5 01 Q ring 0 at June July 39 g differ ent gt tlmes gg gt336 3 039 a year O n 0 Q Conclusion N6 M U fh Additional data not shown indicates the two species lay their eggs oviposit in the same places on plants NQQQ 76 W 33 199 W38 U0 Q 0 3 Muf Qvga The results of this study demonstrated that G cal marien 511a Giquot55 iilEEEEEW6 39a1f b id ii39cai pecies Overall Conclusion that are able to co exist despite frequently encountering 39 iii in Blossey s own n words o p n o r KaliJim fquot A m i a V V m P L s fr v39v 7 if t b a r r13 t 1397 E a El Lr linseed Julialittan J in 4 r m t t J in and i39 9 all ij H o re I M a can 39 V 0 Ag e e pla39n the coe 39stence of SIG with apparently identical niches Key point Competition hypothesis makes the critical assumption that populations f all species esp strong competitors are in equilibrium meaning they are at steady high numbersat or very near carrying capacity b 4 m AC But what if this were not true plwit Cmmy 0 Jam We are Q we ngg N 4N AW W 11 The Disturbance Hypothesis a nonequilibrium hypothesisgog w0L xquot In some communities populations of many species may rarely Q9130 05 become abundant as a result of frequent disturbances Disturbance a dramatic change in abiotic conditions that reduces densities of some or all populations in a community 0 9f l t 399quot 9 terrestnal systems flre w1ndstorm ood drought frost aquatlc systems spates dryups freeze ups hlgh waves Main effect of disturbance Reduction in population sizes Possible result pop sizes of strong CW may rarely reach point where would drive weaker competitors to extinction small numbers of strong competitor means enough resources left over for weaker competitors to maintain at least a small population Disturbances act like starfish predators discussed earlier The Disturbance Hypothesis in graphical form Imagine you have three species A B C with nearly identical niches and that A is a stronger competitor than B or C When there is no disturbance might expect to see this fww ft W of 3n Size M W at k WWW N f we My A a W K w X t K time gt But if there are occasional disturbances at each i might see 95 L 0 Pop size 1W An example of how abiotic disturbances can increase the number of competitors in a community Ecosystem Boulder fields in the intertidal ll zone of southern California Species Sessile organisms one barnacle and a variety of species of algae that fix themselves to the tops of boulders Critical resource Space sites of attachment on the top of the boulder Type of disturbance Large waves during storms that can roll the boulder buryingkilling attached organisms Note The bigger the boulder the less chance of disturbance 20 Imediumsized E large Percent of 15 boulders that are disturbed each month 5 a mediumsized large Size of boulder The primary species involved arcle Chthamalusfissus Red alga Rad alga I Red alga Gigartina Gigartina RhOdOgZOSSI m a me canaliculata leptorhynchos What usually happens on a bare patch of boulder First siX Colonization by barnacles and the green alga months Next siX Colonization by the red algae species months Within One species of red algae G canalicalata takes over and 23 years dominates occupying 60100 of the surface area 100 7 7 4gt 0 0 mg SIPP l i GIGARTINEE CANAlLIClULAlA i4 u m wgaaa so arm titanium Percent Of 0 O RHUD39DGLUSSUM AFFI NE fr v CHTHAMALUS FISSUS boulder quot 60 z 39 surface quot i covered by the species 40 201 O V ElQJNlD 4FlMlAIMlJJAlslolN lD Jllrll ll 9 xlquot quotkJ ldlhlslolNID lelM 1974 1975 1976 1977 Critical things to note in the graph above The average number of species differs on mediumsized more frequently disturbed and larger rarely disturbed boulders IILDU l Mediumsized B La rge 30 Percent ef ED heullc lere 10 20 U 1 2 3 Mean number ef epeeiee en bDUiMEIF Critical to hate in the abeve graph Why d0 we see this SUMMARY COMPETITION AND COMMUNITY COMPOSITION l Ecologists have long recognized that biological communities are no random collections of species Often there are many species that seem like they could be in a community but for some reason are not in the community 2 What determines the species composition of communities Traditional view interspecific competition for resources plays major role in determining community composition Ecologists have long argued that communities will usually be comprised of species whose niches do not overlap extensively this stems from work of Gause amp others 3 Two basic lines of evidence support the hypothesis that competition a oes in uence what combinations of species occur in communities a often species that do exploit the same basic resource show evidence of niche partitioning ie they use different portions of the resource use the resource in different locations or at different times etc b numerous unplanned quotexperimentsquot showing that species that DO use the same resource in essentially the same way cannot coexist in the same community e g scalesuckers zebra mussels purple loosestrife 4 However there are clearly cases where species with seemingly identical niches no obvious niche partitioning occupy the same community How is this possible One hypothesis As a result of occasional ecological disturbances that reduce population sizes stronger competitors never reach numbers where they are consuming so much of the resources that weaker competitors cannot maintain a population The populations in non equilibrium from disturbance hypothesis is relatively new and still needs extensive testing ECOSYSTEM ECOLOGY Ecosystem the biotic community and physicalchemical abiotic environment combined Foci of study in ecosystem ecology 1 Input output and recycling of essential nutrients Wherehow do different organisms obtain key nutrients including N P Ca Mg S Fe etc As succession progresses and liVing plant matter accumulates nutrients are taken out of the soil and quotlocked upquot in plant tissue How is the soil replenished with nutrients to allow further succession and the production of new plantsanimals Two main routes of replenishment A new supplies of nutrients are constantly imported into community washed in by ooding creeks rivers blown in by the wind eroded off of rocks etc B community quotrecyclesquot nutrients locked up in dead organisms or parts thereof 2 Energy ow through the community and productivity see Lct 11 LECTURE 11 PRODUCTIVITY AND THE FLOW OF ENERGY THROUGH ECOSYSTEMS Productivity the rate at which new living tissue biomass is added to the community Forms of new biomass 1 quotProductivityquot can be measured amp expressed two ways 1 Amount dry mass of organic matter added to the community per unit area per unit time eg kg of dry matter produced per m2 per year or metric tons of dry matter produced per ha per year dry 2 Amount of stored energy added to community per unit area per unit time total energy stored in the chemical bonds of molecules comprising new living tissue energy that is released when tissue is burned thereby breaking all chemical bonds eg kilocalories of chemical energy stored per m2 per year or kJ per km2 per year bomb calorimeter Carnivores lt gtCarnlvores Hanan M 5 Zooplankton Herbivo Plants Phytoplankton a it Gk roducers In most ecosystems plants are the primary producers Plants form the base of the food chain Plants are autotrophs Animals are consumers Animals are heterotrophs Primary productivity productivity of the quotprimary producers quot green plants Plants convert solar energy into chemical energy 12 H20 6 C02 solar energy gt C6H1206 602 6H20 Energy is stored or fixed in form of chemical bonds of carbohydrates specifically glucose Some carbohydrates are used in cellular respiration to produce ATP which is then used to fuel cellular functions quotmaintenancequot Other carbohydrates are used to make new tissue in the processes of growth and reproduction Net primary productivity total energy fixed in photosynthesis total used for maintenance respiration net energy gain Net primary productivity varies dramatically between different types of ecosystems NPP per unit area Algal beds and reefs Tropical wet forest Wetlands Tropical seasonal forest Temperate evergreen forest Estuary Temperate deciduous forest Savanna Boreal forest Woodland and shrubland Cultivated land Temperate grassland Upwelling zones Ocean neritic zone Lake and stream Aquatic Tundra I Terrestrial Open ocean Desert and semidesert scrub Rock sand ice 0 500 1000 1500 2000 2500 Average net primary production gm2yr Secondary productivity productivity of heterotrophs consumers in the community Herbivores 1quot consumers covert net primary productivity new plant biomass into new herbivore biomass Firstorder carnivores 20 consumers convert new herbivore biomass into new carnivore biomass Key point Of all the biomass produced at one trophic level only a small fraction of that biomass is consumed and converted into new biomass by next trophic level up Question If herbivores say only convert a small fraction of the available plant biomass into new herbivore biomass in a given year what happens to the rest of the plant biomass that is produced that year The fate of new plant biomass in a community Assimilatecl r Metabollzed New biemassa Available t hreugh gut productten as feed to New Flam Fquot Ingested 10 pI Uducer by la biemass consumers wall inte bleed growth amp next Implth gees to cells rapmdaerfrm level maintenance Uneaten plant Lost in material feces I Deucamposers censumeiuee this detritus repeated processing untll all energy extracted all chemical bends broken Herbivores convert plant biomass into new herbivore biomass How efficient are herbivores at making this this conversion How much of the new plant biomass does not qet eaten qoes undiqested or is used for maintenance Ecological efficiency The percentage of biomass produced at one trophic level that is converted to new biomass in the next trophic level quotupquot eg efficiency of energy transfer between primary producer plant level and primary consumer herbivore level equals amount of new herbivore biomass producedyr x 100 amount of new plant biomass producedyr eg efficiency of energy transfer between herbivore level and secondary consumer small carnivore level equals amount of new secondary consumer biomass producedyr x 100 amount of new herbivore biomass producedyr Ecological efficiencies are estimated to be on average no more than in most communities What this means Say 5000 kg of new plant biomass is produced in a community each year and average ecological efficiency is 10 Maximum amount of new herbivore biomass produced Maximum amount of new small carnivore biomass is produced Maximum amount of new large carnivore biomass is produced This is an average varies with type of organism insects can be efficient fish can be efficient while birds and mammals are normally efficient Low ecological efficiencies has a dramatic effect on the number of organisms in each trophic level Results of two studies where researchers actually counted the number of organisms in the community that belonged to di erent trophic levels NUMBER OF 39 39 TROPHIC LEVEL INDIVIDUAL ORGANISMS 3 Tertiary consumers 354904 Secondary consumers 708624 Primary consumers 5842424 f Producers Michigan bluegrass eld DRY WEIGHT TROPHIC LEVEL g m2 15 Tertiary consumers 11 3 Secondary consumers 37 39 Primary consumers 809 Producers Florida bog Critical fact about these two communities that is true about all other biological communities Why are big fierce predators ie the tertiary and especially the quaternary consumers so rare 1 Tertiaryquaternary consumers are usually large warmblooded organism like birds and mammals Because they are warmblooded and use much energy to maintain a high body temperature they convert less food into new tissue than other types of organisms eg insects fish amphibians reptiles Principle of Allocation Energy that goes into maintenance can t be used for the production of new biomass growth and reproduction But there is a second more important reason Large carnivores Small carnivores Herbivores Plants Top Carnivore Primary Carnivore Herbivores W umm Pyramid of Momma in a TerresMaI Ecosvsrem Why some stop world hunger advocates hate cows Energy flow in a com eld and a feed lot Figures are per growing season Sunlight 2043 million kcal Re ected Converted to Heat etc ff 39 i 2010 million kcal Gross 39 Plant Primary 39 Photosynthesis Production 33 million kcal Corn Respiration 54 million kcal Net j New Com Primary Protoplasm Production 266 million kcal Stalks Husks Cobs Roots 184 million kcal Grain 82 million kcal The grain may be consumed in some form by man If instead it is fed to cattle to produce beef the energy ow continues Not Assimilated 12 million kcal Assimilated 39 by Cattle 70 million kcal Respiration of Cattle 58 million kcal I New Proto lasm Secondary P P d ti s of Cattle 1quot C m 12 million kcal 3941 Waste in Processing etc 08 million kcal Y Human Food in Form of Beef 04 million kcal Summary of figure to the left Humans are omnivores and can function as herbivores or as carnivores Humans Hurfmns Cattle Plant matter PlantTmatter rain 9 grain Total food energy obtained from 1 hectare cornfield 82 million kcal Total food energy available to humans if functioning as herbivores 82 million kcal Total food energy in form of beef if feed corn to cows 04 million kcal Ecological efficiency of the corncow feedlot system Meat energy 0A x 100 49 Corn energy 02 Percent of food energy lost in the conversion of corn to beef 951 Perennial Questions 1 How did there come to be all these diff types of living organisms on Earth 2 Why is each organism quotstructuredquot the way it is And why does each org anism seem to be quotdesignedquot for it39s environment 3 Where do humans t in LECTURE 12 PREDARWINIAN VIEWS ON THE ORIGIN amp DIVERSITY OF SPECIES Creationism predominant view until 1859 quotorigin of speciesquot published all species created in one short interval of time about 6000 years ago by some higher being a Creator all organisms designed by Creator to fit perfectly into their assigned habitat and lifestyle eg quote from W Swainson s 1835 zoology textbook Treatise on the Geography and Classification of Animals It appears that various tribes of organized beings were originally placed by the Creator in certain regions for which they are by their nature peculiarly adapted species are immutable ie unchangeable Because Creator was unable to make a mistake so there would never be a reason for perfectly created species to change their form Mutation or adaption would imply that the Creator made a mistake all organisms eXIst to serve man eg We have horses to do labor we have plants to feed man misquitos teach man humility Fossil organisms with no apparent living representatives on Earth a challenge to the creationist view Crassygyrinus a fossil vertebrate from Scotland All life was supposedly created in perfect form by a Supreme Being So how could any forms of life fail ie go extinct French paleontologist Georges Cuvier39s 17691832 theory of catastrophism During the Earth s history periodic catastrophes including giant mudslides oods earthquakes etc buried and destroy Whole groups of organisms ie all representatives of certain species causing the extinction of whole species sigh wig QrM Ql xgz igs C x I JeanBaptiste Lamarck 17441829 9 gab iv o Paris Museum of Natural History KL coins the term Biologythe study of Lifequot o Accomplished botanist invertebrate zoologist philosophy of zoology o 1809 publishes book Philosophie Zooogique in which he puts forth two big ideas both of WhICh assume specres are not Immutable Nu gym 1 Species are constantly transforming themselves into more complex higher forms of life 2 Species can change their form to to changes in their environment was Lamarck39s theory of transformism W Again He is first to seriously challenge idea of species immutability These snails illustrate a smooth series of intermediate fossils from the oldest known ancestors to presentday forms The transitions along the way are gradual often making it dif cult to divide the lineage into distinct species Do the above represent six separate fossil species Or has one species changed its form over time He writes After a long succession of generationsindividuals originally belonging to one species become at length transformed into a new species distinct from the first DNQ wico S pal s 9quot He is correct but takes things way too far9 5W W he believed all animals are striving to a 39higher39 form W 5 S L eg Worms to insects reptiles to birds etc W QMCQS rm 31 WM as Basics of Lamarck s Theory of Transformism 1 Very simple microscopic organisms are continuously being quotspontaneously generatedquot out of bits of inanimate material dust dirt etc through quotelectrical actionquot and quotheatquot Nature by means of heat light electricity and moisture forms direct or spontaneous generations at that extremity of each kingdom of living bodies Where the simplest of these bodies are found 2 Some simple 39 TABLE organisms are gradually SHOWING THE ORIGIN OF THE VARIOUS ANIMALS transformed into another mm mm more complex type of m m organisms and then into 39 even more complex type of organisms etc Insects Amhnida Annelids Crustaceans 3 All organisms strive for 3311 increased complexitv but 39 only certain organisms mm attain higher states Wu pinnacle of complexity is the human species Hulda Man assuredly presents the Hammm39 Am phaan Mammals type of the highest perfection that nature could attain hence the more an animal s organization approaches that of man the more perfect it is View Mammals Ungulate Mammals Unguiculate Mammals How amp why does transformation of organisms into quothigherquot more complex and perfect forms occur WA cm gec h m 501Mquot According to Lamarck for change exist within every species Nature in successively producing all species of animals beginning with the most imperfectand ending her work with the most perfect has caused their organization gradually to become WWO it C Nature gives to animal life the power of progressively complicated organization Lamarck believed that if Nature natural forces were powerful enough to produce life from nonlife through lightning and heat then Nature could do just about anything once the di tcult step of spontaneous generation is made no important obstacle stands in the way of our being able to recognize the origin and order of di erent productions of Nature Lamarck s Theory of Transformism the idea that species change into Whole new species and types of organisms is never taken seriously based on a lack of evidence and the fact that his internal forces idea was considered unscientific Lamarck is much more famous for his ideas on how species change form to adapt to changes in their environment See next 9 7 0 0 V wv g S N 2 as a o39 w o Am 7 M 0 Mom meolt3ra43 5 at vamp 3 P63 0 Lamarck on How Animals Adapt to NewChanged Environments VVhy do we Win form among organisms Lamarck also argues organisms can not only transform to higher creatures but they also have the capacity to change quotadapt39 to special conditions in local environment creates diversity in form Lamarck proposes two mechanisms of adaptation 1 Adaptation through quotfelt needs sentiments interieurs Organism s bodies subconsciously sense a need for new beneficial traits and over successive generations they develop these traits indiv39s in species feel a need for an adaptive trait produce it and pass on the GiraffesLamarcl s hipst amgusgxamplg g g aquiredtraits gtAncestor of giraffe probably resembled modern day Okapi giraffes closest living relative Okapi gt Lamarck argues giraffe ancestor continually stretched to reach leaves high up on trees j if t Giraffe gt constant stretching of neck quotsensedquot or felt by the body gt consequently body produces o spring w slightly longer necks than themselves gt process repeats itself until neck of the right length achieved critical note parent organisms do not change themselves but because they can subconsciously sense a need for a change they produce o spring with the bene cial change Lamarck promotes idea of what eventually is called induced mutation 2 Adaptation through Principle of Use and Disuse and Law of Inheritance of Acquired Characteristics i Principle of Use and Disuse quotThe frequent use of any organincreases the functions of that organ leads to its development and endows it with a size and power that it does not possess in animals which exercise it less Lamarck felt not only did muscles enlarge with use but other structures and organs as well eg Lamarck39s argument for how deer antlers first appear ancestors of deer had no antlers males could not fight with their teeth had weakjaws resorted to butting their heads together caused there to be more bone and hard matter on their skullcapseventually develop horny protuberances In his own words Since ruminantshave little strength in their jaws the y can only fight by blows with their heads attacking one another with their crowns In the frequent fits of anger to which the males especially are subject the efforts of their inner feeling cause the fluids to flow more strongly towards that part of their headthere is hence deposited a secretion ofbon y matter mixed with horny matter which gives rise to solid protuberances thus we have the origin of antlers Lamarck also said while the constant disuse of such an organ imperceptibly weakens and deteriorates it progressively diminishing its faculties until finally it disappears eg many cave animals are blind Lamarck argues that disuse of eyes leads to their degeneration In his own words Animals which habitually live in places where light does not penetrate have no opportunity of exercising their organ of sight There are found among them some which have lost the use of this organ and which show nothing more than hidden and covered up vestiges of them it becomes clear that the shrinkage and even disappearance of the organ in question are the results of permanent disuse of that organ GiftMme 3M6 low 3 Law 4 Inlrux cm OA MG M Ovmmol l w ii Law of Inheritance of Acquired Characteristics Characteristics that parents acquire during their lifetimes are inherited by offspring Now every change wrought in an organ through a habit of frequently using it is subsequently preserved bv reproduction Such a change is thus handed on to all succeeding individuals without their having to acquire it in the same way that it was actually created Blacksmith39s large upper bodies son39s also had large upper bodies Lamark saw as evidence of this theory Lamarck combines the Principle of UseDisuse and the Law of Inheritance of Acquired Characteristics to explain adaptations eg gt through constant use headbuttingl each generation of male deer increases the size of the antlers slightly gt offspring inherit the slightly enlarged antlers gt process repeats itself over and over until some endpoint I F immunityum go from this if gradually toIIgt Lamarck39s idea for how some birds developed webbed feet individuals in a species of shorebird with simple unwebbed toes for some reason move into the water begin to swim swimming stretches the wee bit of skin between their toes offspring are born with already stretched bit of skin between toes process repeats itself over and over until bird evolves large amount of webbing between the toes Lamarck argues modern birds show various transitional stages Northern phalarope frigate bird Important note Lamarck proposed two mechanisms by which organisms adapted to their given environment ie developed traits that enhanced survival growth and reproduction in their particular environment 1 His Principle of Felt Needs eg giraffe 2 His Principle of Use and Disuse combined with his Law of Inheritance of Inheritance of Acquired Characteristics Do not hybridize the two mechanisms Key difference between the two is how offspring acquire new beneficial traits In his Felt Needs mechanism the parents sense a need for the trait but don39t develop it themselves they give birth to offspring with the trait In UseDisuseInheritance of Acquired Characteristics The Law of Inheritance of Aquired Characteristics on the other hand says that the parent developes the traits and then passes them on to the child IIrJ 1gt LECTURE13 CHARLES DARWIN AND HIS THEORY OF quotDESCENT WITH MODIFICATIONquot FOR THE ORIGIN AND DIVERSITY OF SPECIES companion to the captain sails 27 Dec 1831 to map the coast of South America oSpends much of his time collecting describing plants amp animals wherever the Ship makes port 0 Returns to England 5 yrs later becomes a semireclusive scientist Western isles AMERICA 32 North 39 39 39 Atlantic Ocean British isles Q 3 North 39 quot 39 5 Q Pacific Ocean Canary is North 39 Cape Verde ls Paci c Ocean quot I a c a 1 Q 39 39 39 f lslands indian Ocean 5 a 4 Keeling is bkmac 39 Mauritius Bourbon Is Galapagos is e Afarmionis St Helena Mar uesas a aquot Cl I M 39Society is R quot Friendly is i st eunii quot Rio de Janeiro 39quot Montevideo r 39S39ands Buenos Aires Cape of New South I Good Ho P9 HOW Zeaiand Pac f c Ocean Port Desire South 5 Falkland Is Afi n Ocean Straits of 39 euih Magellan Cape T39erra del Fuego Pamfic Ocean Horn Bay of l 24 November 1859 publishes The Origin of Species by Means of Natural Selection M05 6 359 van S Robert Fitzroy captain of HMS Beagle proponent of Natural Theology Natural Theology the idea that one can learn of God and God s Plan by studying the wonders of his Creation One major tenet of Natural Theology Argument by Design proof of god39s existance can be found by examining the fascinating adaptations of plants and animals in nature the argument for the existence of a supreme being by Design of organisms being so fit their environments There cannot be design without a designer order without choice arrangement without anything capable of arranging Arrangement implies the presence of intelligence and mind quotes from the book Natural Theology or Evidences of the Existence and Attributes of the Deity Collected from the Appearances of Nature by William Paley 1802 In short the idea here is that the quotwonders of naturequot the incredible way in which organisms are designed to fit into ie survive and reproduce in their environments essentially proved the existence of a omnipotent creator Darwin is wellversed in Natural Theology as a young man I do not think I hardly ever admired a book more than Paley s Natural Theology I could almost formerly have said it by heart But he will eventually abandon its principles Fitzroy went insane perhaps the trip with Darwin being a catalyst The Two Fundamental Ideas put forth in The Origin of Species 1 The different species of organisms on Earth have arisen through a process of We a W7 may quotion from other previously existing species 2 Modification in the noral for of a species occurs through a process called MW ml WW UK DESCENT WITH MODIFICATION Darwin argues vast array of different types organisms were notoreated in one fell swoop Rather Species have quotdescendedquot from other species existing earlier in time quotdescendedquot meaning directly derived from through 9 an unbroken chain of ancestors cP W a eg first amphibian descendedfromatype of fish 0x1 afgx N Pair of some 03 050 species ofgtoffspringgtgrandgtgreatgtmany thousandsgtearly fish offspring grand to millions of amphibian offspring generations ife ERE IWW 30 r f if 53 r as I39 n 39dil 39 a 39l ik ig a 39 gy quotIlln I f Over the course of the many generations Normal quotformquot of individuals in this quotlineagequot gradually changes from the quotfish formquot over to the quotamphibian formquot doscmbih m Moog gown Darwin39s view History of life on Earth analogous to q9 6 great tree with many many branche time Yaquot 3 5 ch 9 quot Similarity in quotformquot 039 M i x Form refers to morphology physiology behavior and especially genetic makeup etc Couple other points Most species go extinct 98 of all species that have ever lived have gone extinct Darwin knew when he came up with this that all life on earth could be traced back to a single form of life he assumed a simple singlecelled organism Remains a question in biology how did life begin Example of hypothetical ancient cat species Say it arises in Europe 35mya as a small mammal spreads into arctic nland ukraine and savannah of africa Vastly different abiotic and biotic conditions potential food sources These different populations will become modi ed adapt to be better suited more t to that speci c environment arctic dwelling cat becomes like the lynx not very big thick coat stubby extremities huge paws that act like snowshoes east africa dwelling cat becomes like the cheetah this population evolves a larger body size long legs and evolves spaced out vertebrae allowing maximum exibility run fast eurasian steppe dwelling cat evolves to hunt baby mammoths become relatively large most distinct is the very long daggerlike canines rather than throttling the animal the tQ Ei nfii i bi lli eo thje ih r aalPii apl gd bnbbe giB9 ttii PrriEYnE i QEPEBbcies 1135 Repf ia Avb I Mamhnla lia E vanwww i t sx 439 lotW i W g gggoa 5m gas crazy m ge g WWW gczduata E 53 m Jm W o l quot dwr d r f derm i fquot mttla 39 g 39 xi H 9 ii i I I e n faithoi idrlpltiai r l I A 39f I fquot y I in r y w s V p W i I n v 39 mm We piazza p a 09 v A f 39 mg E i Elation l 43939 39 mfg939 O 1 9 0wi 3 I I v 1quot 5 x 01 A s w F39 39 39 a r Lax531 031 b w 1 39 39rquot vu1x 4 r Am hibm H 138 4 Ella t f W39N we 39 i H 7 41 a 1313 i x39 aquot x 39 39 22 A M3 2quot1 39 3 extinct Mt 3 99 gm g dead 39 5quot ifhixgyy 39 a no longer Monor nna v present 51m zycmm ie 39 species w 5 WWW mm Layaway ff fmmym extant N u m i39f 39gt quot quot 39quot 39 039 Ami2quot 7 currently Faultycardla living species Thismwas czeated by mst aeckel in 1856 not long after publication of Darwin s Or the Ozigirz GfSpecies In this early tree of life it is suggested that halisaurid reptiles gave rise to modern crocodilians What does this mean Some type of halisaurd evolved into the organism we would call a crocodilian The tree also proposes that the dinosaurs are descended from some early type of reptile called a thecodont What does this mean the rst type of dinosaur evolved from some type of thecodont V a v 7 Kr i f 39c39 39 u N 37 EA 39 i K x t 9 quotquot 4 Thus between A and B immense gap of relation C and B the finest gradation B and D rather greater distinction Thus genera would be formed How Darwin39s view differed from the prevailing view at the time Each species was not specially individually created but is derived from an earlierexisting species life began as just one species Species are not immutable rather the normal form of a species can change through time to point that a new species has developed Definition Of quotBVOIUtiOI Iquot the change in the normal form of an organism over the course of generations usually in response to a change in the environment D ch t p WV Newquot 2MP 9 Note Form organism s morphology physiology behavior If 03 We Ma W M amp 6x131 cm A Side note Phylogeny phylogenetic trees and evolutionary relatedness a phylogeny iS the evolutionary history of a group of organisms usually displayed in a phylogenetic tree Example of a phylogenetic tree Asiatic American Brown bear Polar bear Sun bear Sloth bear Specmdecl Giant Raccoon Rad black bear black bear bear panda panda If 5 L Ple15tocene Pliocene 1039 Miocene 15 20quot 25439 Millions of years ago 30j 39 Oligocene 35 4039 What it means when we say two species are closely related Means they are descended from a common ancestor in the relatively recent past phylogenetic trees are philosophies based on best evidence THIS WILL BE ON STUDY GUIDE4 Recently published 2008 updated phylogeny Key to the scienti c for bears based on similarity of mitochondrial names DNA T ornatus Spectacled bear M ursinus Sloth bear 0 4quot w g g 3 a 8 a U U thlbetanus ASlath black 2 m c 3 E D 3 bear g 3 S 9 g U o D N c D LU quot O O 3 U americanus American CD Q 0 K 5 39N D C Q E E m m g 8 0 black bear 8 3 w m E E CB 5 U IN E 339 I D 5 3 H malayanus Sun bear U maritimus Polar bear U arctos west Brown bear Grizzly Kodiak from western hemisphere U arctos east Brown bear European Siberian from eastern hemisphere U spelaeus Cave bear recently extinct convergent evolution sh like shape of dolphin What caused Darwin to develop his theory of quotDescent with Modi cationquot for the origin and diversity of species Observations made during his 5year odyssey on HMS Beagle nudge Darwin towards the idea that species are not immutable Some examples 1 Similarity of some fossil and living species at the eg armadillos at one location in coastal South America Extant armadillo 2 Extinct glyptodont Glyptotherium 39 V 4 t l w 1quot z I I F u quot It 39 r l quot 39 J 391 l Lquot in y 9 r J Knit x at g 394e t FM 53 be A u n a 39 o 39 A t i it rrffqi t LW 27 XL Ill During the voyage of the Beagle I had been deeply impressed by discovering in the Pampean formation great fossil animals covered with armour like that of existing armadillos It was evident that such facts as these as well as many others could be explained on the supposition that species gradually become modified from Darwin s private autobiography and the subject haunted mequot I I fcolllection of islands 2 Resemblance of specres on different volcanic Island archipelagos not to each other but to species on nearby continents 55mm Vic J3 Beagle stops at many volcanic Island archipelagos m eg Cape Verde Islands off nw coast of Africa in s Atlantic eg Galapagos Islands off nw coast of S America in Pacific Darwin notes that abiotic environments on different volcanic archipelagos near the equator are quite similar Leads him t0 initialy eXpeCti should basically contain the same or similar species because of similar abiotic conditions Darwin was assuming creationism specially created individual species INStead ndsquot is that the species on the islands resemble the species39 on the nearby mainland not other island species Summarizing his observations in an 1845 book Darwin writes It is probable that the islands of the 7 v H 7b their physical conditions i the Galapagos Islands than the latter physically resemble the coast of South America yet the aboriginal inhabitants of the two groups Vigill ll WM 77 39 those of the Cape de Verd Islands bearing the physical impress of Africa as the inhabitants of the Galapagos Archipelago are stamped with that of South America Cape de Verd group resemble in all L At one point shortly after the voyage as he was beginning to work out the concept of Descent with Modification he also wrote Did the Creator make all new species on oceanic islands yet using forms from the neighbouring Continent ptzl This fact speaks volumes My theory explains this but 5Nquot no other will Years later in the Origin of Species published in 1859 he will use his observations as evidence that species evolve from other species He begins to build his case Why should the species which are supposed to have been created in the Galapagos Archipelago and nowhere else bear so plainly the stamp of affinity to those created in South America There is nothing in the conditions of life in the geological nature of the islands in their height or climatewhich resembles closely the conditions of the South American coast in fact there is considerable dissimilarity in all respects quotJ ld What about the finches of the Galapagos 999 quot W m 0 L QM b a The Galapagos Islands 501 I I W 9 W r 2quot COCOS o DARWIN b WOLF l I 9 I Q a GALAPAGOS m 39 WA 1quot N P39INTA Q MARCHENA O Q GENOVESA woo Emator 0o IAHTOLOHE OCAE BAIHIRIDGE FERNM DMA acm39LEj O APHNE quotMOB as vmom DIPHNE MAJOR HAB39DA BALTRA r EDEN39 PLAZAB PENZONE I SAN CRISTOBAL ISABELA m mum C3 SANTA FE 1 5 a Tomqu 1 FHAMPIOH FLOHEANA 0211235 50 km I I I GARDNER H I L J 1 QGARDHEH 920 W 91 900 I I 1 03035 Camamymtus 9239 psittaCUa Have 14 species endemic to the Galapagos scattered about the various islands Each species differs in the siie and shape of its beak differences related to the type of food eaten Mainly plant lood Z QB Geospiza magniroslns Cermidca Gill3C 98 Mainly animal food k 39ul 394 i 1 l r 100 animal food Closest living relative of darwin39s nches a medium sized medium beaked grassquick nch Current thinking on the origin and evolution of Danvin s nches based on research done over the last several decades Genetic evidence suggests that all species are descended from a common ancestor that inhabited western South America Thought that individuals of an ancestral finch species reach one island that has different types of food than found on mainland The population on this island gradually changes in form as it adapts to feeding on different types of foods eventually becoming different enough to be a new endemic species Later some individuals are transported to a different island with a different environment and different food sources This population evolves into yet another species This process repeats itself over and over ultimately we are left with 14 similar but each with a different form esp beak and each feeding on primarily different foods ADAPTIVE RADIATION Little group gets blown away from mainland colonize an E island 39ROCAO IAMIIIDGE cowuv Arms MINOR aSEYMOUR RABIOAO mums muon Overtime adapt to the food available on the island sz N Q SAN CRISIOBAL SABELA Q SANTA FE 39 L08 HERMANOO 3 I ORTUGA Darwin collected some nches but did not think much about them Did observations of the finches stimulate Darwin to develop his theory on the origin of species as is commonly thought No Although many have been led to think this because of statement Darwin makes in book published in 1845 9 years W The most curious fact about these finches is the perfect gradation in the size of the beaks in the different species Seeing this gradation and diversity of structure in one small intimately related group of birds one might really fancy that from an original paucity of birds in this archipelago one species had been taken and modified for different ends But he also wrote elsewhere in 1845 I have not as yet noticed by far the most remarkable feature in the natural history of this archipelago it is that the different islands to a considerable extent are inhabited by a different set ofbeings and he went on to say I did not for some time pay sujftcient attention to this and had already partially mingled together the collections from the islands OMG When he collected specimens of different types of finches he failed to note which specimens came from which island Big mistake and I never dreamed that islands about sz or sixty miles apart and most of them in sight of each other formed of precisely the same rocks placed under a quite similar climate rising to a nearly equal height would have been differently inhabited Never thought there would be different forms of the same bird on such similar islands In summary The preponderance of evidence suggests that all of Darwin s critical ideas including the whole notion that species on Earth today are the modified descendents of species that existed earlier were worked OUt ier he r9turned to England arrives back when he is around 27 years old His writings suggests that by the time the voyage ended he was only starting to think that species are not immutable as he once thought he was becoming convinced that species can change their form The rest of his Descent with Modification idea would not be worked out until after he returns to England Indeed three species of mockingbirds that Darwin encountered on the Galapagos seem to have had more of an influence on his thinking than did the finches see next page and study guide On three diff islands three diff forms of mockingbirds More influential The mockingbirds of the Galapagos Galapagos Mockingbird of Floreana Mockingbird of Isabela Island Floreana Island V coloration is different 1 quotart I i K big Q f9 one more y thing that f makes him San Cri tobal Mockingbird quest39on 395 of San Cristobal Island beliefs Darwin writing in 1836 I have four specimens there will be found to be 2 or 3 varieties Each variety is constant in its own Island When I see these islands in sight of each other amp possessed of but a scanty stock of animals tenanted by these mocking birds but slightly di ering in structure amp lling the same place in Nature I must suspect they are If there is the slightest foundation for these remarks then the zoology of Archipelagoes will be well worth examining for such facts would undermine the stability of Species By varieties DanVin means originating from a single form just like different breeds of dog we have today originated from one ancestral form Fundamentals of Descent with Modification Darwin works out his ideas on the origin of the different species on Earth shortly after returning from his voyage He will argue Species on earth today are the descendants the modified descendants of other species existing earlier in time Evolution changemodification in the normal form of an organism over the course of generations W Evolutionary changes in form can be so substantial that new species or whole new types of organisms eventually develop Why does modification of a species occur Modifications are not random but rather result in the species becoming WMto new environmental conditions e better able to We and re roduce Adaptations of a 14395 fit cactus A saguaro cactus exhibits adaptations to its ablOth env1ron 1 Flowers a entice ment waxy stem coating shallow M pollinators root system low surface areato a wJ volume ratio and to its biotic environment spines to keep away herbivores owers to attract cuticle if V prevents water loss quot Low surface area to Polllnatofs I 39 volume ratio minimizes 1 evaporative water loss To better survive grow and reproduce it contract with water it Eavailability Shallow root system collects water after infrequent rains L read out in all directions 39 quot 39 to neure max absorbtion of in Trunk is quotpleatedquot so that it can expand when there frequent rains is more water allows trunk to expand without breaking adaptationadaptive trait a morphological physiological or behavioral trait or feature that enhances an organism s ability to survive and reproduce it its given environment un t will die out taking their in as In fit to one s enVIronment less t traits with them out of the gene Mg m or p h ClogCal thSIOIOQicaI or bDehaQiorgl tramts that DenhgnceIDOO the ability t0 SUNV9 and reproduce in particular environment Adaptive Radiation Rapid developent of multiple new species each with a unique adaptive form within a single evolutionary lineage eg Darwins nches cat spreading out across world example from previous lecture etc iAn evolutionary lineage is a group organisms descended from a common ancestor Adaptive radiation occurs when organisms havew W that is opportunities to exploit a variety of new resources l39equot new niches islands perfect for this bc few competitors This can happen when organisms move to new geographical areas esp areas containing few potential competitors eg islands eg small population of finches accidentally arriving on the Galapagos Islands which had few landbirds e g Anolis lizards on Caribbean islands see text 6 g marsupial mammals in Australia see below This can also happen when an organism evolves a new innovative morphological trait that allows it to live in new areas and thus exploit different resources eg evolution in a lineage of fishes lungs that would permit living mostly on land first amphibian evolved limbs lungs and can now exploit whole new niche eg evolution in a lineage of amphibians of an egg that could develop on land allowing for a life away from the water Q irst reptile Massive adaptive radiation of amphibians from a single ancestor who gained a new adaptive trait Note In an adaptive radiation new species can develop simultaneousy when different populations of a species located in different geographical areas adapt to local abiotic and biOtiC conditions at roughly the same time e g hypothetical cat example used earlier sequentialy when a new species evolves then a population of that species moves to a new area and evolves into a new species and this is repeated over and over e g Galapagos finches Note also microevolution In the W adaptive radiation produces a group of closely related species that are quite similar in form eg Galapagos finches Anolz s lizards on Caribbean islands see text Can also have adaptive radiation as a result of environmental changes opening or closing a niche selective pressure causing the species to adapt Over a w of time through a series of adaptive radiations descendant species can evolve into a e g amphibians reptiles birds and the marsupial mammals of Australia see below Type of mammal 250mya mammals evolve from a certain type of reptile 85m years later split in mammilian lineage placental and marsupial Vast majority of mammals are placental I I All marsuplals are descended from a smgle ancestral spaces of marsupial that somehow reached the mammalfree island continent of Australia A series of adaptive radiations have resulted in the great diversity of marsuplals present today evolved a new way of reproducing young born very mall and immature make their way to a structure commonly a pouch 39 with nipples and the youth will crawl if into the pouch and stay there for quite a few months to nish ANTEATER Myrmecoblus FLYING PHALANGEFE Peiourus WOMBAT Phoscolomysl MOLE Notoryciesl 39 NATIVE CAT Dosyurusl39 Dosycercus TASMANlAN WOLF I Thylooms 60mya some type of marsupial made it to the island Adaptive radiation of the marsupials pouched mammals in Australia beginning about 60 million years ago when Australia separated geogiiaphically from Asia The original mar supia ancestor thought to resemble the North 39 American opossum invaded many different C n U n e nt Of ecological areas reproductive isolation and di A U St ra l a W h C h vergence resulted Modified from Simpson and Beck Life2d ed New York Harcourt Brace huge va rlety from a had no land Immv dquot 1965quot single ancestral species mammals marsupials radiate out ORlGINAL OPOSSUMLIKE ANCESTOR CONVERGENT EVOLUTION IN TWO GREAT LINEAGES OF MAMMALS Note Marsupials also provide examples MW development of similarity in form among organisms that are not closely related as a result of adapting to similar ecological niches Placentals I Marsupials Tasmanian wolf Thylacin us Wolf Cams Petaurus E Flying squirrel Glaucomys Worn bat Ground hog Phascolomys Marmora Anteater Myrmecophaga Anteater Myrmecobius Mole Notoryctes Mouse Dasycercus Austrailia has grasslands like NA has grasslands In NA evolution of large grazing mammal Austrailia had a giant kangaroo 7ft tall 500bs but were hunted to extinction by humans Sabertoothed cat evolved to speci cally eat these kangaroos very similar to placental sabertooth Lecture 15 will be evidence for evolution but before that Why do species evolve into new forms LECTURE 14 FURTHER NOTES ON DESCENT WITH MODIFICATION THE ROLE OF ENVIRONMENTAL CHANGE Darwin Modification of a species evolution occurs in a response to changes in the environment Two Ways Species Can Experience quotChange in Environmentquot 1 Chanqe in environment can be caused by movement of individuals to new qeoqraphical location 2 At any single location biotic and abiotic environmental conditions will change over time Example Movement of some darkskinned populations of ancestral humans from Africa to n Europe and Asia For some reason humans became the quotnaked apequot lost their hair dark skin adaptation gttKechhanges intabidtic nvitonntienttas a result f mve north to this 1 Long period of lessened sunlight for half of the year 2 Cold humans wear more clothing which covers their skin gt Critical result Skin produced less melanocites became lighter gtWhy problematic Increased risk of vitamin D deficiency Vitamin D is essential for bone growth 0 Bone is comprised of hard mineral calcium phosphate 0 Vitamin D is essential for synthesis of protein that transports Ca and P through lining of small intestines into bloodstream for transport to bones Epidermal cells include melanocytes make melanosomes and quotgivequot them to surrounding cells help to protect against UVB radiation Vitamin D in some foods but mainly humans produce themselves ty elof causes chemical reaction converting the cholesterol C O CStCI Ol UV radiation to become pre Vitamin D in keratinocyte gt inactive gt1ivergt kidneysgt active cells of skin USGd to Start Vitamin D Vitamin D the process of conversion 80 UV radiation is beneficial but don t need much per day In sunny climates skin receives a dangerous excess of UV radiation can cause skin cancer Skin thus protected by pigment melanin However in northern locations the melanin prevented enough UV radiation to start producing vitamin D caused diseases like ricket5 1800519005 we started fortifying milk with vitamin D One symptom rickets Skin pigmentation Very light 1 lt12 Light 112 14 15 17 Medium 18 20 21 23 Dark 24 26 27 29 Very dark gt29 Micro vs Macroevolutionary Change microevolutionary change in form less dramatic change occurring over relatively short period of time that does NOT result in the evolution of what would be considered a new species or major type of organism microchange in form of species macroevolutionary change in form more dramatic change occurring over relatively long period of time that is so extensive it results in what would be considered a new species or even whole kind of organism macrochange that results in a new species Move north stimulates a microevolutionary change in populations that moved Key point movement by some pops to new geographic location 9 results in change in certain environmental conditions 9 which leads to an evolutionary change in form 2 At any sinqle location abiotic and biotic environmental conditions will chanqe over time Change may be rapid and abrupt happening in a few years or less or change may be gradual happening over tens of millions of years Changes in a species abiotic environment would involve changes in normal level intensity of factors such as temperature precipitation light levels salinity current speed etc Changes in a species M environment involve 0 change in the type nature of available food sources quotpreyquot 0 change in the type nature of interspecific competitors for resources predatorsherbivores parasites and pathogens Examples of rapid changes in a species biotic environment eg The organisms of lsle Royale eg HIV in the human population eg Snakes in tropical Australia see next page An Example of Evolution Australian redbellied black snakes adapt to the invasion of toxic cane toads Cane toad Bufo marinas Native to Central South America Produces milkywhite secretions from parotid glands behind eyes nasty cardiotoxin Voracious appetite introduced around world to help control pest insects esp in sugar cane Brought to NE Australia in 1935 to control cane beetles Now distributed over 12 million km2 Kills most native snakes attempting to eat it Question Have native snakes adapted to this change in their environment Using highly susceptible redbellied black snakes Ben Phillips and Richard Shine of the University of Sydney test for changes in 1 morphology body size 2 physiology toxin resistance 3 behavior avoidance of cane toads as prey Redbellied black snake Pseudechis porphyriacus 17150 17155 PNAS Decemberll d i vo101 no49 Adapting to an invasive species Toxic cane toads induce morphological change in Australian snakes Ben L Phillips and Richard Shine School of Biological Sciences A03 University of Sydneyr New South Wales 2006 Australia PROCEEDINGS OF 39 Pm R Soc B 2006 273 15454 550 THE ROYAL doi101098rspb20063479 SOCI ETY Published online 21 March 2006 An invasive species induces rapid adaptive change in a native predator cane toads and black snakes in Australia Ben L Phi ips and Richard Shine School of Biological Sciences A08 University of Sydnw NSW 2006 Australia Rapid environmental change due to human activities has increased rates of extinction but some species may be able to adapt rapidly enough to deal with such changes Our studies of feeding behaviour and physiological resistance to toxins reveal surprisingly rapid adaptive responses in Australian black snakes Pseudechr39s porphyriocus following the invasion of a lethally toxic prey item the cane toad Bufo marinas Snakes from toad exposed localities showed increased resistance to toad toxin and a decreased preference for toads as prey Separate laboratory experiments suggest that these changes are not attributable to learning we were unable to teach naive snakes to avoid toxic prey or to acquired resistance repeated sub lethal doses did not enhance resistance These results strongly suggest that black snake behaviour and physiology have evolved in response to the presence of toads and have done so rapidly Toads were brought to Australia in 1935 so these evolved responses have occurred in fewer than 23 snake generations Morphology Body size Hypothesis Snakes will evolve larger bodies in areas with toads Rationale Analysis Compared mean size of adult snakes SNV snout to vent length in areas that have had toads for different lengths of time statistically controlled for other variables that might in uence snake size like climate Results 1200 1000 Mean SNV 30quot quot SE 600 in mm 200 0 l l I 0 5101520253035404550 Key point Exposure time to toads in years Physiology Toxin resistance Hypothesis Snake populations with longterm exposure to toads will show an increased tolerance to toad s cardiotoxin Methods Compared 13 snakes from populations with 560 years of exposure to toads vs 28 snakes from pops in toadfree locations Measured swimming speed of snakes before and after nonlethal oral dose of toxin calibrated to body size 80 p g of toxin per g of body mass Analysis Calculated and compared percent reduction in swimming speed Results 60 quot39 Statistics t 33 o 0 df 39 O P 0009 40 g g t 9 E 20 Q 0 t O o L O 0 O 2 I I naive exposed exposure category Resistance to toad toxin in toadexposed and toad naive populations A large percentage reduction in speed indicates low resistance to toxin Hence snakes from toad exposed populations exhibited higher resistance to toad toxin Also compared percent reduction in speed vs years of exposure to toads 60 Statistics F 102 0 df 112 P 0009 40 E 3913 8 E 20 quot 51 2 5 3 quotCI 8 0 i O 20 I 1 I 39 I I I I 0 10 2039 I 30 40 50 60 70 time since rst exposure years Resistance to toad toxin as a function of the time a snake population has been exposed to toads A large percentage represents a low resistance Hence the snakes resistance to toad toxin increases with increasing exposure time Behavior Tendency to eat cane toads Hypothesis Snakes in populations with longterm exposure to toads will show an evolved innate avoidance of toads Methods Captured 12 snakes from populations with 4060 years of exposure to toads vs 12 snakes from pops in toadfree locations After 3 wks offered each snake a freshly killed nontoxic frog and a toxic toad in random order 3 days apart Gave 24 h to consume Results 100T 333333 933333 Statistics g X2 56 3333333 3 0014 it 754 333333 e 39 W 3939393939393939393939 39 E 5 3333333 3 a 50 5 IIIII quot5 at 433333 E 25 3333331 3 IIII a i l a 39 0 J exposure to toads The percentage of black snakes from toad exposed and toad naive populations Willing to eat a toad or a frog No snake from a toadexposed locality would consume a toad Error bars represent a standard error Note Is avoidance of toads a learned trait or a genetically based instinctiveinnate trait Further work showed that snakes fed a small toxic toad were no less likely to feed on frogstoads when later given a chance This suggests that the avoidance of toads is a genetically based instinctive trait Evolution as a result of unnatural selection A Bighorn sheep Ows anode1515 have experienced selection from hunters who prefer large males with long horns 8 Over the past 30 years this unnatural selection has resulted in the evolution of shorter male horns Adapted from Coltman et al 2003 B 80 1 E w 3 Equot 6 I 39 51quot O 2 F g 50 1 5 o C e E 40 o E 30 n ev 1970 1975 1980 1985 1990 1995 2000 2005 Year o Female 0 Male 2222 No data available g g Atlantic cod have experienced 5 decades of selection for smaller 5 body size as a result of selective E harvest by fisheries ie preference 5 0 for largerbodied fish 1 w Individuals now reach sexual 8 maturity at a significantly smaller 2 body size than they did 50 years ago 3 Although larger individuals are more fecund there is now a major selective disadvantage in waiting until a large body size is attained 2 1 1 1 1 1 1 1 1 1 1 1 before reproducing 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 Year A NOTE ON THE AGE OF THE EARTH Darwin recognized that modification of species in response to environment change is a very slow process and thus if all species on earth descended from single inaugural species the earth must be way older than 6000 years which some said the Bible indicated Some geologists in Darwin s day were already arguing that the earth was older than that We now know that life has been on earth for at least 3 billion years Major periods and extents in the history of life on Earth are represented in In calendar on which a quotdayquot lasts about 150 million years On this scale Hum sepreirs evolved 1n the last 10 minutes of day 30 and recorded historv I39S CWquot fined to the final 30 seconds I elfquotam motraQ39 I 239 3 4 5 hikgnn 3 D E IA 0 N I Firsttire 39 Vast coat 6 39239 39B 9 10 11 12 forests 39 AIRCIlEAN39EON Oldest eukaryotic fossils Oldest mu lticel iu iar fossils l 39t MESOZOJC CENOZOIC ERA ERA First flowerin plants Rise of mammal Home reprints First true First hominids Remrdm bug th last 10 minutes humans last 30 seconds of day 30 of day 30 First amphibians bDrb NIH I91 MOS39ISOSQXWE LECTURE 15 EVIDENCE THAT SPECIES EVOLVE DESCEND FROM OTHER SPECIES EVIDENCE IN THE FOSSIL RECORD fossil impression or remnant of an organism that lived in the past organism dies in mud or sand organism 39 caStS ImpreSSIOnS Of Orgamsmsrots but impression remains petrified organisms or parts of organisms organism dies in W 02 P39acev body turns to stone never unpetrified organismsparts in ice or ambgr g n decomposes in arctic ice or in pine tree sap that hardens into a rock encasing the organism Richest source Of IOSSIISI sedimentary FOCk root word is sediment forms when sediment in bodies of water brought in by rivers or 0 Rivers bring sediment to the tributaries falls down to the ocean Sedimentary rocks containing fossils form on bOttOm layer Of the bOdy Of water hardens over time into rock Settles in layers which can 9 Over time additional st ta are added containing f sils be used to date fOSSIIS39 from each time period 6 As sea levels change and the seafloor is pushed upward sedimentary rocks are exposed Erosion by rivers reveals strata older strata contain older fossils 39 the ocean floor W Younger stratum with more recent 09 60 fossils the weight of a the i SECIII TIent 39 resses Q Older stratum p LIV 7 with older fossils down and Strata Plural compresses 0 Strutum Sin ular W9 p g erosion can then expose 82 strata as tectonic activity occurs over time Most of the land of north america very low elevation was covered by water for about 300 million years sediments build up all that time Tectonic activity caused plates to squeeze together forming mountain ranges and draining away water exposing sedimentary beds to erosion The process of fos silization Fossilization can occur in many ways Here a dead gazelle lies on the shore Soft tissues quickly decay and only skeletal remains are left After the water level rises sedi ments settle on the remains of the gazelle producing anoxic conditions needed for fossilization Adapted from Larsen 2008 A gazelle dies on a lakeshore rAft r iheVLSOfttissu e remains OEZthfe ig zellleE dgqayEpply 39 ifhe39skel fonisflref i The water level of the lake rises and thelake sediments settleand cover the gazelle s bones The bonesfossiliize in the I thick Iayerof sediment at v the bottom of the lake whilesediments continue to be deposited as layers The lake dries and other geologic processes occur A volcanic eruptiongfor example spews ash over theeregion providing more layers Themssil isnowernbedcied in agedogic stratum Erosion exposes deep Strata in a geologic columnrevealing the fossilized skeleton Scientists use radiometric dating to determine an age of organisms or rock and create a geologic record record of earth39s history 1 Different types of organisms f39r f in the fossil record at very Win the Earth39s history KatSPENle Millions Duration of Years in Time Before Millions Scale Present of Years eon Era Period Epoch approx approx Organic Events Recent last 7 7 7 7 7 i Quarternary 5000 years 16 Appearance of humans 1 Pleistocene 164 39 Pliocene 35 Dominance of mammals and birds Cenozoic Miocene 185 Proliferation of bony shes teleosts a i 255 a r n Rise of modern urou s of mammals Trtm a i g p 6 law thocen 105 and invertebrates 54 w J Eocene 21 Dominance of owering plants Paleocene 7 10 Radiation of primitive mammals 05 65 p 9 Gretaceous 81 Extinction of dinosaurs I 3 146 t r r r 7 UL g Mesozmc 7 Rise of giant dinosaurs g 1 Jurassilc 62 A y a 7 y b 3 ppearance of rst birds 5 203 e E Triassic 57 Development of conifer plants 9 245 7 t 7quot Proliferation of reptiles Permian 45 Extinction of many early forms invertebrates i 290 I 41 1 Pennsylvanian 30 M DID Carboniferous 320 39 7 a 77 W D Mississippian 776 4395 Development of amphibians and insects I We r r 7 7277 3 395 7 77 7777 W Paleozoic 46 t 5 i 1 r v r Hamill l r if DV x 9 L a i i 3 Di Silurian r r 439 30 First land plants and land invertebrates Ordovician 66 Dominance of inverteprates r 1 9 9 a M j Ils39kkt39h 7 by 4 Sharp increase in fossils of invertebrate Cambrian V0 40 h l A P Y a v a 545 quot Upper 900 355 Appearance of multicellular organisms Proterozoic Middle 700 Appearance of eukaryotic cells x 1600 7 7 U a v Lower 900 A earance of lanktonlc rolca otes E 2500 pp p P Y i f in a Archean MOO Appearance of sedimentary rocks SUBK quot 6 quot E quot 39 matolites and benthic prokaryotes 0 an 3900 w 770 From the formation of earth until rst Hadean 600 appearance of sedimentary rocks no observable fossil organisms QVij quot Wbc Lg MQM 0 W 80 ModA5 SWSQ M09 35 FOLiqg m 4W3 k In regards to the fossil record The Creationist hypothesis predicts That the fossil record should show representatives of all species in rocks of all ages Since all species were created at the same time In contrast Darwin s Descent with Modi cation hypothesis predicts That the fossil record shows different types of organisms will appear in different aged rocks since they evolved from other more ancestral organisms O NQ 361 3506 s kg x v V5 inclng o 6Q A 0 amp 0 w 0v 5 x a 2 WMDW39M soulse 5 S VWM WAL RM Qb ms39 quotThe explanation lies as I believe in the extreme imperfection of the eologic recordquot 2 More evidence arwm s proposal predicts occurrence of Wittoi a 39il Oll many examples exist in the fossil record transitional form a fossil organism whose morphology suggests that it was an intermediate in the transition between I one major type of organism to another famous fossnl archeoptrlx Recent example Transitional forms in the evolution of whales What makes a whale a whale Penn Femur is f Y v Cervical vertebrae of a dolphin Defpbinus delpbis Delphinidae l7ff397 Only the axis and atlas are fused whereas was 1 f i I k o I v if W L of the series are fused in some cemceans fully aquatic cannot rlU 7 7 propel themselves by moving tail up amp down lower vertebrae modified to enhance this ability eg lower vertebrae not fused together amp large neural spines to give leverage to large tail muscles compressed cervical vertebrae give very short neck perhaps adaptation to nostrils moved up back form blowhole reduce drag lower mandible and inner ear bones modified in structure and position to enhance ability to hear underwater sound resonating in the bone hairless although hair appears in fetuses of some species can be unusually large animals A stunning number of spectacular transitional forms have been discovered since 1990 These forms show that evolution of modern whales began 6555 millions of years ago mya SS 50 45 4 I 0 35 30 ZS Millions of years ago Hippopotamus Transitional forms bt land and marine I I Wquot I mammals 4 Ancestor of whales most likely looked similar to this Moved into water md b u to take advantage I onywa V quot around middle eat Of empty mChe Or Fmshwawsemi to av0Id predation aquatic habitat Whales evolved in the eocene 3555 mya Largepowerfultail Shorter legs Fat pad in jaw for hearing Bradcish water habitat Salt water habitat Nasal opening shifted back Eyes on the side of head Tailflukes Very small hind legs Nasal opening shifted further back Etholocation for hunting si Complete loss of hind legs Nasal opening reaches position of blowhole in living whales Baleen for filten39ng food Similarities in certain morphological features suggest that whales descended from some type of artiodactyl a mammal with an even number of hoofed toes For example compare the structure of the ankle bone in the ancestral whale Rodhocetus and a modernday artiodactyl the pronghorn Antilocapra Rodhocetus Antilocapra Comparison of ankle bones of Rodhocetus with those of an pronghorn Antilocapra Note presence of 1 a doublepulley astragalus bone which connects to the tibula and fibula 2 a notch in the cuboid for insertion of the calcaneum and 3 a large convex fibular facet on the calcaneum This complex of characteristics is not found in any other type of extinct or extant mammal What does this suggest Rodhocetus and Antilocapra share a common ancestor These two types of mammals whales and artiodactyls have same anatomy bc they are descended from a common ancestor with that same anatomy To see how and why these transitional forms are transitional we can compare the skeleton of Mto that of an early type of artiodactyl W Note Eomyrex is too young to have been the ancestor of whales but the structure of its skeleton is thoughuo he similar to that of the true artiodactyl ancestor of whales Two reconstructions of Elomeryx by different zoological artists Skeletons of Elomeryx Rodhocetus and latertransitional form Bpmdon i u N5 ii y I l L n39 u l w t Lw nampr Put crudely the transitional form should be half land animal and half marine should share traits and morphology with both types of organisms 511 57 L L M 77 n 37 t h a Ej f I U r arr hl u ll a J a VA r r 777 lmk L J 1 Lin 7 i 1 Snakes not well understood bc of lack of transitional forms an organism found that is fossorial habits burrows suggesting that snakes evolved from burrowing lizards Science progresses in little increments Ardipithecus ramidus found one of the socalled quotmissing linksquot that tells us how the human form evolved from an ape ancestor FOR THE EXAM Figure out why this is a transitional form bt ape and human Was it a knucklewalker Descent with Modi cation All existing species are decended from previously existing species Older artiodactvllike terrestrial traits still retained in Rodhocetus nostrils still mostly low amp forward just above canines pelvis attached to backbone and still functional hind limbs still functional large neural spines on thoracic shoulder vertebrae suggest animal was still supporting weight on land with forelimbs Newer whalelike traits of Rodhocetus that continue to an even greater degree in Dorudon pelvis much reduced in size limbs esp forelimbs shortened sacral vertebrae near hip not fused not visible in picture and have somewhat enlarged neural spines for attachment of large tail muscles suggesting tail is used in locomotion much shortened cervical vertebrae giving short neck modification of lower jaw to aid in underwater hearing not visible in picture increase in size Rodhocetus 3 m long Dorudon 6 m long EVIDENCE FROM THE quotCOMPARATIVE ANATOMYquot OF EXTANT SPECIES 1 In many groups of organisms there are striking similarities in the anatomy of structures used for very different purposes One of best examples forelimb of different types of mammals Human Cat Whale Bat Humerus Humerus Radius Humerus 39 Carpal l 1 l 2 39 3 All tetrapdds have a basic pentadactyl five digit limb structure The fore timbs of a bird human whale and bat are ail constructed from the same bones even though they perform different functions Key point Why puzzling to early anatomists Solution to the puzzle Same numberarrangement of bones would be expected if all mammals are descended from an organism with same arrangement of bones in its forelimb Strong evidence detailed series of transitional forms indicates that all mammals are descended from a single species of cynodontian reptile fwgg wa 39 x u 9 i a D 39 393 g 393 4quot 9 I t 24quot U 39 quot II 5 ag Note the structure of the forelimb in this cynodont quotWhat can be more curious than that the hand of a man formed for grasping that of a mole for digging the leg of a horse the paddle of a porpoise and the Wing of a bat should all be constructed on the same pattern and should include the same bones in the same relative positionsquot Charles Darwin 1859 in The Origin of Species Important terminoloqv homoloqous structures We say that two structures are homologous if a one structure is the quotmodified descendentquot of the other e g the wings of a bat are modified forelegs e g colorful ower petals are modified leaves e g teeth of fish are highly modified scales once found in the region of the mouth your teeth are descended from fish scales too b two structures are similar because they are both derived from the same structure in a common ancestor e g earliest fossil mammal had hard claw or naillike structures on their digits just like their cynodont reptilian ancestor your ngernails the claws of a bear and a horse s hooves are all derived from the same reptilian nailsclaws and hence are all homologous The opposite of homologous is analogous Analogous structures are structures that are similar because of convergent evolution ie adapting to the same basic niche The structures evolved independently Examples gt Wings of bats and wings if birds gt The saber teeth of placental sabertoothed tiger and the saber teeth of the marsupial sabertoothed cat 2 Lack of engineering perfection in anatomical design eg Suboptimal positioning of entrances to trachea amp esophagus Hard palate Soft palate Bolus Orepharynx Tongue Epiglottis Laryngepharynx Larynx a b Deglutition 3 Position of structures prior to degiutition b During degiutition the tongue rises against the oaiate the lawnx rises the epiglottis seals off the larynx and the bolus is passed into the esophagus 7qu A descended lar A ynx exacerbates the choking haz ard in humans A In nonhuman mammals such as the dog shown Epgloms here the epiglottis reaches the soft palate effectively sealing off the mouth cavity whenever the trachea is open B In humans the larynx is positioned much lower This ta Soft palate cilitates Speech production by the passage of air through the mouth Soft palate but it comes at the expense of not Epiglottis blocking the ow of material from the mouth even when the tracheal opening is exposed Food Tongue Esophageal sphincter Epiglottis up contracted Larynx Esophagus Trachea To lungs To stomach Esophageal sphincter Epiglottis down relaxed Esophagus Anatomy of the throat trachea and esopha gus The pathway through which air passes from the nose to the tra chea and lungs crosses the pathway through which food or water passes from the mouth to the esophagus and stomach By closing down like a trap door the epiglottis provides a safeguard against accidently taking food into the trachea If epiglottis malfunctions food can lodge in entrance to trachea and a person can choke to death suffocate Why do we have this seemingly maladaptive design see the detailed supplemental lecture notes that posted on course website FIGURE 1 4 Vestigial and atavistic tails Top left in our relatives that have tails such as the ruffed lemur Varecia variegates the tail caudal vertebrae are unfused the rst four are labeled C1 C4 But in the human tail or coccyx top right the caudal vertebrae are fused to form a vestigial structure Bottom atavistic tail of a three month old Israeli infant X ray of the tail right shows that the three caudal vertebrae are much larger and more well developed than normal are not fused and approach the size of the sacral vertebrae SISS The tail was later surgically removed I have given the evidence to the best of my ability and we must acknowledge as it seems to me that man with all his noble qualities with sympathy which feel for the most debased with benevolence which extends not only to other men but to the hamblest living creature with his Godlike intellect which is penetrated into the movements and constitution of the solar system with all these exalted powers Man still bears in his bodily frame the indelible stamp of his lowly origin Charles Darwin Atavism the reappearance in an individual of a characteristic of some remote ancestor that has been absent in intervening generations further evidence that species evolve from other species 3 Presence of quotvestigialquot structures vestigial structure Functione55 or near functione53 structure often small amp rudimentary thought to be a remnants of a previous evolutionary state examples vestigial pelvis and hind limb in whales ear muscles and 3rd molars wisdom teeth in humans quotsplintquot bones vestigial toes metacarpals in modern horses I v Second Medial and Fourth Lateral Metacarpals Third Metacarpal Proximal SesamOids Proximal Phalanx Middle Phalanx Distal Phalanx Distal Sesamoid Not Visible quot Due To Distal Phalanx Copyright 3 Jonathan Me39rm 2W3 How do we explain occurrence of vestigial structures A Phylogenetic History of Horses MIOCENE39 OLiGOCENE39 39 39 39 EOCENE PLIOCENE PLEISTOCENERECENT 39 iE ib I v Higp idium 39 and other genera39i A d r A h 1 ST EE E EE 39 bhiw HTppa aai f LAEWTPFS 1 H quotI i JPOh EBESJ mgmt l L 39 393939 H I i M5quot YCQ EEEE ypohippuss 39 39 institheriumf 139 A 231 w 1 L MW Parahibpm K L ieslohipp J h a wLH I Hymcotheriunlf Note Horses have evolved from being a digitigrade to unguligrade animal meaning that they changed from running on the balls of their feet to the tips of their toes single toe in the case of modern horses This greatly increases stride length and hence running speed Foot Posture We have just seen that runners have relatively long leg bones But it is the e ectz39ve iength of the legmthe part that contributes to stride iength that is important and this can be further increased in other ways The human foot does not contribute to the Iength of the ieg unless one rises on tip toes The heat is on the ground as one stands and strikes first in each stride Bears opossums raccoons and most other vertebrates that walk well but seldom run have similar feet Such feet are called plantigrade 3 sole walking Running dinosaurs birds carnivores and extinct ancestors of hoofed mammals increase effective leg length by standing on what corresponds to the ball of the human foot These animals are digi grade finger walking Perissodactyis artiodactyls and the cursoris representatives of severai extinct orders of mammals have like the ballet dancer further increased effective leg length by standing on the tips of the digits This foot posture is unguligrade hoof waiking which is why these animals are called ungulates Where foot posture and limb proportions are ach modi ed for the curso n al habit the enhanced length and slendemess oi the leg skeleton is striking pmnnsaaoe BEAR memeame ooe UNGULIGRAUE DEER CONTRAST IN PROPORNONS AND FOOT POSTURE in the left hind leg skeieton of a nonmrsor left moderate cursor center and highly specialized cursor right Gradual loss of all but 1 toe in horses leaving vestigial splint toes Hyracotherium Miohippus Mewchippus Pliohippus Equus Eocene Oligocene Mlocene Pliocene Pleistocene Science seeks the truth And it does not discriminate For better or worse it finds things out Science is 39 0 humble It knows what it knows and 39 it knows what it doesn t know V It bases its conclusions on beliefs on 39 hard evidence that is constantly updated and upgraded It doesn39t get o ended when new facts come along It embraces the body of knowledge It doesn 39t hold m I i onto medieval practices because they are tradition If it did you wouldn39t 9 lgg BQQQF get a shot of penzczllzn when you got 5 14 3 j N g a nasty venereal disease you pop a leech down your trousers and pray Comedian Ricky Gervais How science works Start with some interesting unexplained observation or phenomenon 1 Alternative explanations hypotheses are proposed 2 Predictions are generated from each hypothesis lithe hypothesis is true then we should see 3 Predictions are tested via observation and experiment research 4 Hypotheses notsupported by the evidence are rejected 5 The hypothesis receiving the most support is accepted as the explanation most consistent with the facts and evidence but 6 Standing hypotheses can and should be repeatedly retested AND New hypotheses can and should be proposed and tested at anytime as more information becomes available PREDICTIONS Phenomenon 18th century Creationist Doctrine on Origin of Species Darwin s Explanation Descenth Modification Pattern of species appearances inthefossH record Similarity in the anatomy of appendages used for very different purposes in closely related species PREDICTIONS 18th century Creationist Darwin s Explanation Doctrine on Origin of Species Descenth Modification Perfection vs imperfection in the design of organisms Presence of vestigial structures I have steadily endeavored to keep my mind free so as to give up any hypothesis however much beloved and I cannot resist forming one on every subject as soon as facts are shown to be opposed to it quot Charles Darwin A3 W An example of how abiotic disturbances can allow the coexistence of multiple competing species in the same niche Ecosystem Boulder fields in the intertidal V j zone of southern California Species Sessile organisms one barnacle and a variety of species of algae that fix themselves to the tops of boulders Critical resource Space sites of attachment on the top of the boulder Type of disturbance Large waves during storms that can roll the boulder see below The primary species involved 1 Qt D n 39 l 39 1 0 1 x39 9 39 39 l quot393 gt 391 39 j V o 7quot 37 X arnacl i I Green alga Ulva l ye alga Chthamalus flSSMS Gelidium coulteri X E 39 391 Red alga Red alga Red alga Gigartina 53 Gigam39na Rhodoglossum a me canaliculam bLp 5 qu leptorhynchos What usually happens on a bare patch of an UNDIS T URBED boulder X First siX Colonization by the green alga Ulva and a barnacle 0 Off a months Chthamalas fissas the fastest colonizers Why 0512 Next siX Colonization by the red algae species slower to colonize months bare rock but grow taller and choke out green algaebarnacles Within One species of red algae G canalicalata a thick tall species 23 years eventually takes over and dominates occupying 60100 of the surface area on undisturbed boulders 7 C9 39 VJ Wm UVTXD v we a v v Wm OJ 9 CW Example of what happened overtime on the newly exposed hare surface of one boulder that went undisturbed for gt 2 years 100 80 Percent of boulder surface 6393 quot covered by the species 40 20 a O 75 Signs 1974 1975 Critical things to note in the graph above 9JF1Ml MlJldIAISIUlN lD mum SPF wrestling ICANAHLIC a GiIGAIRl INlA LIEPTUHHYNg gg IULATTA gngLuM CDUMEE O O RHUDOELOSSUM AFlFI NE V V lil lM LUS 1135115 r o 77x 7 J 1 1p 7 000A b5 2 m quot duu JF1MAWEMJASMDHND 1976 umM 1977 Again in this community disturbance results from large waves turning over boulders Two e ects of boulder rolling That may scrape off some organisms creating bare patches on the boulder Or the boulder may be completely overturned all the organisms get buried in sand boulder is now bare on top Note The smaller the boulder the greater chance of disturbance 20 Percent if 15 lbeuillldlers tlhat are dlietuirlltiedl M each mentlh 5 U l I mediumsized large Size of buulder What is the e ect of a higher rate of disturbance on the richnessdiversity of species on individual boulders individual communities Higher disturbance means higher diversity because bare patches allow other species to grow instead of strongest species Opens up resources for other species to come in and exist The average number of species differs on mediumsizil more frequently disturbed and larger rarely disturbed boulders 100 I Mediumsized n 21 boulders observed 80 r E Large n 37 boulders observed Percent of 50 boulders of observed 40 20 1 2 37 Mean number of species on boulder Critical to note in the above graph Medium sized boulders tend to have a larger number and diversity of species on them Larger boulders tend to have lower diversity only one species Why do we see this The disturbance removes or kills some of the stronger competitor opening up space for the weaker competitors Does not allow strong competitor to build up numbers SUMMARY COMPETITION AND COMMUNITY COMPOSITION 1 Ecologists have long recognized that biological communities are no random collections of species Often there are many species that seem like they could be in a community but for some reason are not in the community 2 What determines the species composition of communities Traditional view interspecific competition for resources plays major role in determining community composition Ecologists have long argued that communities will usually be comprised of species whose niches do not overlap extensively this stems from work of Gause amp others 3 Two basic lines of evidence support the hypothesis that competition does in uence what combinations of species occur in communities a often species that do eXploit the same basic resource show evidence of niche partitioning ie they use different portions of the resource use the resource in different locations or at different times etc b numerous unplanned quotexperimentsquot showing that species that DO use the same resource in essentially the same way cannot coeXist in the same community e g scalesuckers zebra mussels purple loosestrife 4 However there are clearly cases where species with seemingly identical niches no obvious niche partitioning occupy the same community How is this possible One hypothesis As a result of occasional ecological disturbances that reduce population sizes stronger competitors never reach numbers where they are consuming so much of the resources that weaker competitors cannot maintain a population The populationsinnonequilibriumfromdisturbance hypothesis is relatively new and still needs extensive testing SUMMARY COMPETITION AND COMMUNITY COMPOSITION 1 Ecologists have long recognized that biological communities are no random collections of species Often there are many species that seem like they could be in a community but for some reason are not in the community 2 What determines the species composition of communities Traditional view interspecific competition for resources plays major role in determining community composition Ecologists have long argued that communities will usually be comprised of species whose niches do not overlap extensively this stems from work of Gause amp others 3 Two basic lines of evidence support the hypothesis that competition does in uence what combinations of species occur in communities a often species that do eXploit the same basic resource show evidence of niche partitioning ie they use different portions of the resource use the resource in different locations or at different times etc b numerous unplanned quotexperimentsquot showing that species that DO use the same resource in essentially the same way cannot coeXist in the same community e g scalesuckers zebra mussels purple loosestrife 4 However there are clearly cases where species with seemingly identical niches no obvious niche partitioning occupy the same community How is this possible One hypothesis As a result of occasional ecological disturbances that reduce population sizes stronger competitors never reach numbers where they are consuming so much of the resources that weaker competitors cannot maintain a population The populationsinnonequilibriumfromdisturbance hypothesis is relatively new and still needs extensive testing
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